You asked about day tripping from Athens (or Piraeus).

I hope a Ziner with on-the-ground experience can answer you. However in the meantime, I found a couple of sites that might help: http://www.athensguide.com/aegina.html It talks about Hydra (sounds great!) http://www.greeklandscapes.com/greece/hydra.html

BTW, it is a 40 minute trip by public transit from Athens to Piraeus, according to one site. Here's the local transit authority page showing the possibiities. http://tinyurl.com/7klvs

Frances Toronto, Canada